Summer solstice

People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Eric Thayer (UNITED STATES - Tags: HEALTH SPORT SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SPORT SOCIETY TPX IMAGES OF THE DAY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY SPORT)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY SPORT)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SPORT SOCIETY)

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A woman poses for her friend as they take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SPORT SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Eric Thayer (UNITED STATES - Tags: HEALTH SPORT SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY SPORT)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SPORT SOCIETY)

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Traffic is pictured between groups of people taking part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY SPORT)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Eric Thayer (UNITED STATES - Tags: HEALTH SPORT SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Eric Thayer (UNITED STATES - Tags: SPORT HEALTH SOCIETY)

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A woman takes part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Eric Thayer (UNITED STATES - Tags: HEALTH SOCIETY SPORT)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY)

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People take part in a group yoga practice during the afternoon of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Shannon Stapleton

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SPORT SOCIETY TPX IMAGES OF THE DAY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson (UNITED STATES - Tags: HEALTH SOCIETY TPX IMAGES OF THE DAY)

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. The "Solstice in Times Square" event on Friday brought out thousands of participants to celebrate the year's longest day in New York. REUTERS/Lucas Jackson

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Revelllers celebrate the pagan festival of 'Summer Solstice' at Stonehenge in Wiltshire in southern England, on June 21, 2013. The festival, which dates back thousands of years, celebrates the longest day of the year when the sun is at its maximum elevation. Modern druids and people gather at the landmark Stonehenge every year to see the sun rise on the first morning of summer. AFP PHOTO / JUSTIN TALLIS

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Revellers celebrate the summer solstice at the ancient Stonehenge monument on Salisbury Plain in southern England June 21, 2013. Stonehenge is a celebrated venue of festivities during the summer solstice - the longest day of the year in the northern hemisphere - and it attracts thousands of revellers, spiritualists and tourists. Druids, a pagan religious order dating back to Celtic Britain, believe Stonehenge was a centre of spiritualism more than 2,000 years ago. REUTERS/Dylan Martinez

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Revelllers celebrate the pagan festival of 'Summer Solstice' at Stonehenge in Wiltshire in southern England, on June 21, 2013. The festival, which dates back thousands of years, celebrates the longest day of the year when the sun is at its maximum elevation. Modern druids and people gather at the landmark Stonehenge every year to see the sun rise on the first morning of summer. AFP PHOTO / JUSTIN TALLIS

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A woman takes part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. REUTERS/Eric Thayer

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People take part in a group yoga practice during the afternoon of the summer solstice in New York's Times Square, June 21, 2013. REUTERS/Shannon Stapleton

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. REUTERS/Eric Thayer

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. REUTERS/Lucas Jackson

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. REUTERS/Lucas Jackson

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. REUTERS/Eric Thayer

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Participants practice yoga as part of a series of mass yoga classes set on Times Square to celebrate the summer solstice, in New York, June 21, 2013. AFP PHOTO/Emmanuel Dunand

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People take part in a group yoga practice on the morning of the summer solstice in New York's Times Square, June 21, 2013. REUTERS/Lucas Jackson

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Participants practice yoga as part of a series of mass yoga classes set on Times Square to celebrate the summer solstice, in New York, June 21, 2013. AFP PHOTO/Emmanuel Dunand

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Revelllers celebrate the pagan festival of 'Summer Solstice' at Stonehenge in Wiltshire in southern England, on June 21, 2013. The festival, which dates back thousands of years, celebrates the longest day of the year when the sun is at its maximum elevation. Modern druids and people gather at the landmark Stonehenge every year to see the sun rise on the first morning of summer. AFP PHOTO / JUSTIN TALLIS

Revelllers celebrate the pagan festival of 'Summer Solstice' at Stonehenge in Wiltshire in southern England, on June 21, 2013. The festival, which dates back thousands of years, celebrates the longest day of the year when the sun is at its maximum elevation. Modern druids and people gather at the landmark Stonehenge every year to see the sun rise on the first morning of summer. AFP PHOTO / JUSTIN TALLIS

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Revellers celebrate during the summer solstice at the ancient Stonehenge monument on Salisbury Plain in southern England June 21, 2013. REUTERS/Dylan Martinez

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Revellers celebrate during the summer solstice at the ancient Stonehenge monument on Salisbury Plain in southern England June 21, 2013. REUTERS/Dylan Martinez

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A reveller, wearing a traditional native American headdress, celebrates the summer solstice at the ancient Stonehenge monument on Salisbury Plain in southern England June 21, 2013. REUTERS/Dylan Martinez

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Revellers celebrate the summer solstice at the Stonehenge monument on Salisbury Plain in southern England June 21, 2013. REUTERS/Kieran Doherty

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Revellers kiss as they celebrate during the summer solstice at the ancient Stonehenge monument on Salisbury Plain in southern England June 21, 2013. REUTERS/Dylan Martinez

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A girl takes photos of the Kokino megalithic observatory during the summer solstice celebration in Kumanovo June 21, 2013. The 3,800 years old observatory was discovered in 2001 in the north-western town of Kumanovo 70 km north from capital Skopje and is ranked as the fourth oldest observatory in the world after Egypt's Abu Simbel, Britain's Stonehenge and Cambodia's Angkor Wat according to NASA. REUTERS/Ognen Teofilovski

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A reveller celebrates the summer solstice by placing her hands on one of the stones at the ancient Stonehenge monument on Salisbury Plain in southern England June 21, 2013. Stonehenge is a celebrated venue of festivities during the summer solstice - the longest day of the year in the northern hemisphere - and it attracts thousands of revellers, spiritualists and tourists. Druids, a pagan religious order dating back to Celtic Britain, believe Stonehenge was a centre of spiritualism more than 2,000 years ago. REUTERS/Dylan Martinez

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A reveller gestures as he celebrates the summer solstice at the ancient Stonehenge monument on Salisbury Plain in southern England June 21, 2013. Stonehenge is a celebrated venue of festivities during the summer solstice - the longest day of the year in the northern hemisphere - and it attracts thousands of revellers, spiritualists and tourists. Druids, a pagan religious order dating back to Celtic Britain, believe Stonehenge was a centre of spiritualism more than 2,000 years ago. REUTERS/Dylan Martinez

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Macedonians celebrate the summer solstice at the marker of Kokino megalithic observatory June 21, 2013. The 3,800 years old observatory was discovered in 2001 in the north-western town of Kumanovo 70 km (43 miles) north from capital Skopje and is ranked as the fourth oldest observatory in the world after Egypt's Abu Simbel, Britain's Stonehenge and Cambodia's Angkor Wat, according to NASA. REUTERS/Ognen Teofilovski

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Macedonians celebrate the summer solstice at the marker of the Kokino megalithic observatory in Kumanovo June 21, 2013. REUTERS/Ognen Teofilovski

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A druid mask is seen on Salisbury Plain in southern England June 21, 2013. REUTERS/Kieran Doherty

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A long exposure picture of the Kokino megalithic observatory is seen during summer solstice celebration in Kumanovo June 21, 2013. The 3,800 years old observatory was discovered in 2001 in the north-western town of Kumanovo 70 km north from capital Skopje and is ranked as the fourth oldest observatory in the world after Egypt's Abu Simbel, Britain's Stonehenge and Cambodia's Angkor Wat according to NASA. REUTERS/Ognen Teofilovski

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Revelllers gather to celebrate the pagan festival of 'Summer Solstice' at Stonehenge in Wiltshire in southern England, on June 21, 2013. The festival, which dates back thousands of years, celebrates the longest day of the year when the sun is at its maximum elevation. Modern druids and people gather at the landmark Stonehenge every year to see the sun rise on the first morning of summer. AFP PHOTO / JUSTIN TALLIS

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Revelllers celebrate the pagan festival of 'Summer Solstice' at Stonehenge in Wiltshire in southern England, on June 21, 2013. The festival, which dates back thousands of years, celebrates the longest day of the year when the sun is at its maximum elevation. Modern druids and people gather at the landmark Stonehenge every year to see the sun rise on the first morning of summer. AFP PHOTO / JUSTIN TALLIS

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Macedonians celebrate the summer solstice at the marker of the Kokino megalithic observatory in Kumanovo June 21, 2013. The 3,800 years old observatory was discovered in 2001 in the north-western town of Kumanovo 70 km (43 miles) north from capital Skopje and is ranked as the fourth oldest observatory in the world after Egypt's Abu Simbel, Britain's Stonehenge and Cambodia's Angkor Wat according to NASA. REUTERS/Ognen Teofilovski